OpenSource solutions for "safe surfing"
So you run the network of a school / company etc...
Most of them tools are realy expencive and some block a bit more then you'd want, or too little..
The Children's Internet Protection Act mandates that a school or library must have an Internet safety policy, must hold a public review of that policy and must use a "technology protection measure" on all computers connected to the Internet. Whether and how that software can be disabled on certain computers is a local decision. It does not mandate that software be perfect; indeed, many web pages, both administrative and commercial, emphasized that filtering would not be perfect.
http://www.squidguard.org/ Seems to be a good sollution...
and if you do want to spend (a little) money: http://dansguardian.org/ might be it !!
Read the article about it: http://www.linuxjournal.com//article.php?sid=6807
In one of the comments a person speaks about webcleaner.. http://webcleaner.sf.net/
I tried it at home and must say I'm stunned..
this is propably the best "popup-killer/add-remover" I have ever seen..